OLEDs are a type of light emitting diode in which the emissive electroluminescent layer is a film of an organic compound that emits light in response to an electric current. The organic material is sandwiched between two electrodes at least one being a transparent electrode. OLEDs exhibit high luminescence, high efficiency and require low driving voltage and are therefore good candidates for use in display screens, e.g. for televisions, computer monitors, mobile phone screens, etc. OLEDs can effectively be used for large panel areas and full color displays with extremely high resolution.
However, the use of OLEDs for displays requires special treatment. In particular, exposure to moisture or oxygen can do extensive damage to the organic luminescent layer. Therefore, encapsulation of the OLED is critical to protect the device from moisture and oxygen. There are several methods used for encapsulation, but all of them have disadvantages. In particular, one method of encapsulating OLEDs is to cover the device with a metal or glass layer secured by an epoxy resin. A desiccant material, such as calcium oxide or barium oxide is normally incorporated into the device when using an adhesively attached metal or glass encapsulation layer. This method of encapsulation is high in cost and fairly low in effectiveness. It also results in a final device having a relatively high profile.
Another method of encapsulating OLEDs is to use an inorganic, organic or hybrid layer; e.g. SiNx, SiOx or Al2O3 deposited onto the device. This layer may be deposited by any one of many standard deposition techniques, including chemical vapor deposition (CVD), physical vapor deposition (PVD), or atomic layer deposition (ALD). All of these deposition techniques require temperatures that exceed the normal limits of the OLED device and therefore may damage the device, especially the organic luminescent layer during processing. Further the equipment required for such depositions is costly and deposition times are relatively long thereby adding significant cost to the manufacturing of the devices.
Therefore, there is a need in the art for improvements to encapsulation techniques for OLEDs.